Urban centers in the region feature a high concentration of top-rated universities and highly-skilled, professional jobs, which pushes up earnings.

FORBES: The Best-Paying Cities For Women 2013

However, the top tax rate reductions appear to be associated with the increasing concentration of income at the top of the income distribution.

FORBES: Non-Partisan Congressional Tax Report Debunks Core Conservative Economic Theory-GOP Suppresses Study

Buy ETFs holding the biggest concentration of the top 15 CANSLIM stocks reported in he IBD 100.

FORBES: Backdoor CAN SLIM: ETFs Loaded With LULU, NFLX And BIDU

In 1958, he found the concentration at the top of the volcano to be around 315ppm (that is 315 molecules of CO2 for every one million molecules in the air).

BBC: Carbon dioxide passes symbolic mark

Economists argue about the disincentive effects of higher tax rates. (Messrs Piketty and Saez, the economists who have transformed analysis of income concentration at the top, reckon, controversially, that the optimal top income-tax rate could be as high as 80%.) But no one doubts that there are trade-offs.

ECONOMIST: Policy prescriptions

The Unep assessment said the concentration of mercury in the top 100m of the world's oceans had doubled over the past century, and estimated that 260 tonnes of the toxic metal had made their way from soil into rivers and lakes.

BBC: Nations agree on legally binding mercury rules

The Unep assessment says that the concentration of mercury in the top 100m of the world's oceans has doubled over the past century, and estimates that 260 tonnes of the toxic metal have made their way from soil into rivers and lakes.

BBC: UN: Rising mercury emissions increase risk to humans

And the trend towards concentration of deposits among America's top banks has accelerated as a result of these deals, for example (see chart 3).

ECONOMIST: The contract between society and banks will get stricter

Looking at the Nook for a second, you can immediately isolate the top as the light source, with a stronger concentration and somewhat even distribution.

ENGADGET: Amazon Kindle Paperwhite hands-on (Update: video)